The present invention relates to a system and a method for controlling an idling speed of an engine, and more specifically, for controlling the idling speed by simultaneously adjusting a fuel injection amount and an intake air amount passing through an idling speed control valve to improve responsibility of the control when an engine load varies.
Recently, various engines employ a fuel injection control for an injector and an idling speed control by means of an idling speed control valve provided in a passage bypassing a throttle valve.
In a conventional idling speed control as disclosed in Japanese laid-open patent application No. 60-212648, an error between an actual engine speed and a target idling speed is first calculated, and then an opening degree of the idling speed control valve is changed so as to reduce the error thus calculated, whereby the intake air amount is changed. Moreover, the intake air amount thus changed is detected by an air flow meter and the fuel injection control refers to the detected intake air amount to calculate a fuel injection amount to be injected by the injector, whereby the idling speed is maintained even when an engine load changes due to, for example, the operation of an air conditioner.
Such the conventional control, however, has an unsolved problem that the fuel injection delays since the fuel injection amount is derived after the change in the intake air amount is detected by the air flow meter. Therefore, when the engine load is abruptly varied, such the delay causes large fluctuations in the engine speed. In addition, there is a further problem that when the idling speed control valve sticks at its full open state, the fuel injection amount is excessively increased as well as the intake air amount passing through the idling speed control valve, causing the over-running of the engine even at the idling.